Source Sans Pro seems to suffer from a bug in that the font renders numbers and characters with different heights when both are set to the same font size. The issue affects web pages as well as desktop applications and is more noticeable at given font sizes. The issue occurs at different font sizes depending on the browser; some examples:
Chrome 8, 10, 13, 14, 17, 19, 24, 26, 28, 29, 30, 31…
Firefox 10, 13, 16, 18, 21, 24, 27, 30, 32, 33…
Using the zoom, both on WEB and desktop apps, has the effect of scaling the font, thus either fixing or introducing the problem, depending on the zoom scale factor.
Note: The zoom doesn’t seem to introduce the problem when starting from a scale-safe font size
Internet Explorer
This font is not designed to work with IE, as stated by the google font portal when trying to load the Source Sans Pro page in IE
We thought to baseline on this font, yet are now needing to review our systems as a workaround to try to make sure that no irregular rescaling of the font-size takes place.

Source Sans Pro seems to suffer from a bug in that the font renders numbers and characters with different heights when both are set to the same font size. The issue affects web pages as well as desktop applications and is more noticeable at given font sizes. The issue occurs at different font sizes depending on the browser; some examples:
Chrome 8, 10, 13, 14, 17, 19, 24, 26, 28, 29, 30, 31…
Firefox 10, 13, 16, 18, 21, 24, 27, 30, 32, 33…
Using the zoom, both on WEB and desktop apps, has the effect of scaling the font, thus either fixing or introducing the problem, depending on the zoom scale factor.
Note: The zoom doesn’t seem to introduce the problem when starting from a scale-safe font size
Internet Explorer
This font is not designed to work with IE, as stated by the google font portal when trying to load the Source Sans Pro page in IE
We thought to baseline on this font, yet are now needing to review our systems as a workaround to try to make sure that no irregular rescaling of the font-size takes place.